The present invention relates to the switching of video signals, and more particularly to switching reference generation using a scanning sync separator for switching between video signals of different formats or sync timings.
Existing SMS7000 Video Matrices, manufactured by the Grass Valley Product Group of Tektronix, Inc., only deal with one vertical sync switching reference. This reference is used to define the vertical interval switching point, that is, the point in time where the switch from one signal to another occurs. However a need exists to switch groups of signals having different sync timings in the same video switch matrix, such as systems having both 525 line/60 Hz and 625 line/50 Hz signals or systems containing groups of signals of the same television standard that are asynchronous to one another.
An ideal solution would be to decode vertical sync from each output and use this to generate a unique vertical switching reference for the crosspoint switch that drives the respective outputs. This means that, if a signal present at a crosspoint input is synchronous with the signal currently present at the crosspoint output, a switch to that input is by implication synchronous. A block diagram illustrating this approach is shown in FIG. 1. This architecture is well established and widely used in routing switchers. In analog systems the added cost of a sync separator for each output is relatively insignificant, but with serial digital video routing switchers it is necessary to convert the serial bitstream into the parallel domain in order to detect vertical sync. In a routing switcher containing multiple outputs (destinations), the size, cost and power consumption required to implement this architecture is considerable.
What is desired is a switching reference generation architecture for multiple format or sync timing video signals that minimizes the size, cost and power consumption required to perform the switching function.